The present invention relates generally to inkjet printing mechanisms, and more particularly to an angular wiping system for removing ink residue from an inkjet printhead in an inkjet printing mechanism.
Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as xe2x80x9cink,xe2x80x9d onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a xe2x80x9cservice stationxe2x80x9d mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. To facilitate priming, some printers have priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as xe2x80x9cspitting.xe2x80x9d The waste ink is collected at a spitting reservoir portion of the service station, known as a xe2x80x9cspittoon.xe2x80x9d After spitting, uncapping, or occasionally during printing, most service stations have a flexible wiper, or a more rigid spring-loaded wiper, that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper.
During wiping, it is important not only to wipe the orifice plate in the area of the linear nozzle arrays which eject ink, but also to wipe along the cheek regions of the printhead adjacent the orifice plate as described in U.S. Pat. Nos. 5,980,018 and 6,132,026, both assigned to the present assignee, Hewlett-Packard Company. These patents discuss a system which has nozzle wiper blades dedicated to wiping the orifice plate along the ink ejecting nozzles, and an auxiliary pair of cheek wiper blades located to each side of the nozzle wiper blades. The cheek wiper blades remove debris along the cheek regions of the printhead adjacent the nozzles, and are referred to therein as xe2x80x9cmud flaps.xe2x80x9d The term xe2x80x9cmud flapxe2x80x9d was used because these auxiliary cheek wipers if inverted resemble the rubber mud flaps used on pickups, semi-tractor trailers and the like to prevent mud from being flung from a vehicle""s rear wheels onto a following vehicle.
Use of the auxiliary mud flap wiper blades removed ink residue clinging to the cheek regions of the printhead. If otherwise left untouched, this cheek ink residue often attracted fibers, such as clothing lint or hairs. Such fibers clinging to the printhead often extended down to touch the media in the printzone, and when the trailing fibers were pulled by the carriage through freshly printed ink, they caused the ink to smear leaving horizontal streaks across the printed image, resulting in a print defect known in the industry as xe2x80x9cfiber tracks.xe2x80x9d
As additional components are introduced into inkjet printers for the home, office and business environment, such as various optical sensors like those described in U.S. Pat. No. 6,036,298, currently assigned to the present assignee, the Hewlett-Packard Company. In the home and office environment, the amount of work space consumed by a printer, known as the printer""s xe2x80x9cfootprint,xe2x80x9d is desired to be at a minimum. Use of these additional sensors often increases the overall printer width, increasing the printer""s footprint, requiring a trade-off between providing a consumer with additional features, while still providing a compact printing unit. Use of the auxiliary mud flaps to clean the cheek regions of a printhead to eliminate fiber tracking, in addition to the use of various sensors located in the service station region, in some cases increase the overall printer width up to one inch (2.54 cm). Thus, it would be desirable to find a way to control fiber tracking without increasing the footprint of the printing unit.